Patterned Ground Plane for Inductor Q Factor
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Solution Overview
Problem
Inductors in RFICs face challenges in achieving high quality factor (Q) at high frequencies due to silicon substrate losses and substrate noise, which limits their performance in applications like voltage-controlled oscillators (VCOs).
Innovation Solution
The implementation of a patterned ground plane with etched portions and slots under the conductor helps prevent eddy current flow, reducing magnetic and electric losses, and is coupled to circuit ground to enhance substrate isolation and Q factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a solid ground plane is used under the inductor conductor, then substrate noise is shielded and electrical stability is improved, but eddy current losses increase and Q factor decreases
Solution Approach 1:
The ground plane is segmented into multiple isolated ground segments rather than using a solid continuous ground plane. These segments are positioned beneath the conductor and separated by gaps, which prevent the formation of large eddy current loops while maintaining electrical connection to ground through vertical vias. This segmentation breaks the eddy current paths that would otherwise form in a solid ground plane, reducing energy loss while preserving noise shielding functionality.
Solution Approach 2:
The ground plane structure is made non-uniform with different properties in different regions. Specifically, ground segments are positioned only in certain areas beneath the conductor rather than uniformly across the entire substrate. The gaps between segments are strategically placed to interrupt eddy current paths while maintaining ground connection through vias. This local variation in ground plane quality allows simultaneous achievement of noise shielding and eddy current suppression.
2Loss of energy
If the ground plane is partitioned into separate shields with slots, then eddy current flow is prevented and Q factor improves, but device complexity increases
Solution Approach 1:
The ground plane is divided into multiple discrete ground segments that are electrically isolated from each other by gaps. Each segment connects to ground through vertical vias but does not form continuous conductive paths that would support eddy currents. This segmentation approach prevents eddy current circulation while maintaining a relatively simple fabrication process using standard photolithography and via formation techniques.
Solution Approach 2:
Material is removed from the ground plane to create gaps between ground segments. These extracted regions eliminate the continuous conductive paths that would otherwise allow eddy currents to flow. The gaps are strategically positioned to interrupt potential eddy current loops while maintaining ground connection through vias, effectively removing the harmful eddy current capability without completely eliminating the ground plane functionality.
3Loss of energy
If a patterned ground plane with open center area is used, then magnetic field distribution is maintained and inductor performance is improved, but ground plane effectiveness is reduced
Solution Approach 1:
The ground plane is segmented into multiple discrete segments positioned around the periphery of the conductor rather than forming a solid continuous plane. This segmentation allows magnetic field lines to pass through the center region and between segments with reduced distortion, maintaining better magnetic field distribution for inductor operation. The segments are connected to ground through vias to provide electrostatic shielding while minimizing magnetic field interference.
Solution Approach 2:
The ground plane structure exhibits spatial variation in ground presence - dense ground segments at the periphery and open space in the center region. This local quality differentiation provides electrostatic shielding where needed (at the edges where electric field termination is important) while maintaining magnetic field integrity in the center region where magnetic flux circulation is critical for inductor operation. The via connections provide localized ground reference without creating continuous ground planes that would distort magnetic fields.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The patterned ground plane design significantly improves the Q factor of inductors from approximately 28 at 6 GHz to 38 at 8 GHz, effectively addressing substrate noise and losses, and maintains good magnetic field distribution, making it suitable for high-frequency applications.
Implementation Method 1
Partitioning the patterned ground plane into separate shields and forming slots on each shield help prevent the flow of eddy current on the patterned ground plane
Data Source
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AI summary
An inductor with patterned ground plane is described. In one design, the inductor includes a conductor formed on a first layer and a patterned ground plane formed on a second layer under the conductor. The patterned ground plane has an open center area and a shape matching the shape of the conductor. The patterned ground plane includes multiple shields, e.g., eight shields for eight sides of an octagonal shape conductor. Each shield has multiple slots formed perpendicular to the conductor. Partitioning the patterned ground plane into separate shields and forming slots on each shield help prevent the flow of eddy current on the patterned ground plane, which may improve the Q of the inductor. Multiple interconnects couple the multiple shields to circuit ground, which may be located at the center of the conductor.